Boris Johnson calls for end to 'soft justice'

Boris Johnson, the Conservative London mayor, has attacked justice secretary Kenneth Clarke's plans to offer shorter sentences to criminals, insisting that rehabilitation should take place behind bars.

In an article in Monday's Sun newspaper, Johnson also called on local authorities to introduce a "payment by results" scheme which would see agencies paid to keep former offenders "on the straight and narrow" after they leave jail.

Johnson, who has made cutting crime in the capital a cornerstone of his mayoralty, waded in as David Cameron and Clarke consider the future of a proposal to halve sentences for most offenders who plead guilty at the first opportunity.

"Soft is the perfect way to enjoy French cheese but not how we should approach punishing criminals," Johnson wrote: "It's time to stop offering shorter sentences and get-out clauses".

Clarke was forced to drop paedophiles and rapists from his sentencingplans following a public backlash earlier this month.

He is expected exclude other categories of serious crime but is keen to retain the discount offer as part of his overall sentencing package to stabilise the prison population, which has reached a record 85,000 in England and Wales.

While Downing Street has made clear that Cameron would like to see the whole sentencing proposal dropped, tearing the heart out of Clarke's plans.

The Ministry of Justice estimates that the scheme would save 3,400 prison places, and £130m, a year. That is more than half the 6,000 places and the £210m that Clarke needs to save if his department is to rein in the growth in the prison population as well as meet the Treasury's demand for a 23% cut in his £8.7bn budget.

But London's mayor argues that rehabilitation should take place in jail and that criminals should not be left out until they are reformed.

"Prison shouldn't be about sitting on a mattress, playing video games and networking with seasoned criminals," wrote Johnson. "Prison should change people and if it doesn't they shouldn't be let out. It's the only way we can stop the revolving door of criminality."

The mayor highlights a scheme at Feltham young offenders institution, which has reduced the reoffending rate from 78% to 30%. The Heron unit – launched in conjunction with the Ministry of Justice as part of the mayor's Time for Action programme to tackle youth violence – is the UK's first dedicated resettlement unit for 15 -17-year-olds.

"On the wing we've managed to halve that national youth reoffending rate of 78% by allocating each prisoner an individual 'motivational' member of staff, who helps them sort out their lives during their jail term, then works with them for a year after their release," wrote Johnson. "The prisoners are pushed into further education, helped to apply for jobs and we've even got a few into university.

"If the boys start to commit crimes again, we don't pay the staff. It's payment by results. And it's a powerful incentive. It's not soft but sensible."

Johnson wants local authorities to follow suit by offering payments to agencies who help keep local criminals "on the straight and narrow".

"In short, local councils, police and the criminal justice system need to work hand in hand to stop the spread of people gearing towards a lifetime of criminality – career criminals. It's the only way we can stop the revolving door of criminality."

He added: "Let's all get behind a solution that can really turn around the lives of those entrenched in crime: no rehab, no release."